Total Spleen Cells Research Articles

Restoration of CD8 self‐tolerance in NOD mice by protective Idd9 genes

Diabetes development in the NOD mouse is controlled by multiple susceptibility loci. Congenic NOD mice that contain B10.D2 genes within the Idd9 locus are highly protected from diabetes and we have investigated the mechanism of protection in these mice. To test for the presence of islet specific CD8 effector cells mice were infected with vaccinia virus that encodes the CD8 epitope from islet expressed IGRP (Vac‐IGRP). When NOD mice were infected with Vac‐IGRP they elicited strong IGRP specific CD8 responses but Idd9 congenic mice were tolerant. Analysis of radiation chimeric mice revealed that expression of protective Idd9 genes by hematopoietic cells is sufficient to restore IGRP specific CD8 tolerance. Reconstitution of NOD‐scid mice with CD8 cells derived from young Idd9 or NOD mice mixed with total NOD spleen cells showed that high frequencies of IGRP specific CD8 effectors could develop from Idd9 CD8 precursors. Hence (i) thymic tolerance is not responsible for restored CD8 tolerance in Idd9 mice and (ii) no protection is derived from endogenous expression of Idd9 genes within the CD8 cell. Transfer experiments with NOD IGRP specific 8.3 cells showed that early activation in the pancreatic lymph nodes is unaffected in Idd9 mice. When the long‐term survival of transferred 8.3 cells was tested, in NOD hosts IGRP specific 8.3 cells could be expanded 6 weeks post‐transfer but in Idd9 hosts the 8.3 cells were deleted.

A Leishmania infantum cytosolic tryparedoxin activates B cells to secrete interleukin‐10 and specific immunoglobulin

The immune evasion mechanisms of pathogenic trypanosomatids involve a multitude of phenomena such as the polyclonal activation of lymphocytes, cytokine modulation and the enhanced detoxification of oxygen reactive species. A trypanothione cascade seems to be involved in the detoxification process. It was recently described and characterized a tryparedoxin (LiTXN1) involved in Leishmania infantum cytoplasmatic hydroperoxide metabolism. LiTXN1 is a secreted protein that is up-regulated in the infectious form of the parasite, suggesting that it may play an important role during infection. In the present study, we investigated whether recombinant LiTXN1 (rLiTXN1) affects T- and B-cell functions in a murine model. We observed a significant increase in the CD69 surface marker on the B-cell population in total spleen cells and on isolated B cells from BALB/c mice after in vitro rLiTXN1 stimulus. Activated B-cells underwent further proliferation, as indicated by increased [(3)H]thymidine incorporation. Cytokine quantification showed a dose-dependent up-regulation of interleukin (IL)-10 secretion. B cells were identified as a source of this secretion. Furthermore, intraperitoneal injection of rLiTXN1 into BALB/c mice triggered the production of elevated levels of rLiTXN1-specific antibodies, predominantly of the immunoglobulin M (IgM), IgG1 and IgG3 isotypes, with a minimum reactivity against other heterologous antigens. Taken together, our data suggest that rLiTXN1 may participate in immunopathological processes by targeting B-cell effector functions, leading to IL-10 secretion and production of specific antibodies.

Leukocytes and the kidney contribute to interstitial inflammation in lupus nephritis

Interstitial leucocyte infiltration, a prominent feature of lupus nephritis, predicts deterioration of renal function. We used two models of lupus nephritis in mice, one with chronic spontaneous disease and the other with acute interferon-alpha (IFN alpha)-mediated disease. The latter is characterized by the virtual absence of interstitial infiltration. In vivo migration assays showed that splenic leukocytes from spontaneously nephritic mice tended to migrate into non-inflamed syngeneic kidneys. This was enhanced if the recipient kidneys were already inflamed. Kidneys from both chronically and acutely nephritic mice showed similar ability to recruit splenic leukocytes from chronically diseased mice. Leukocytes from acutely diseased mice, however, failed to migrate into chronically inflamed kidney. Compared with those with chronic nephritis, the kidneys of acute nephritic mice expressed less of the inflammatory chemokine CXCL13/BLC. Moreover, leukocytes from acute nephritic mice displayed impaired migration, in vitro, to T-cell chemokine attractants. This study links leukocyte infiltration to both kidney chemokine expression, and leukocyte chemotaxis to kidney-expressed chemokines.

Single-Cell Analysis of FVIII-Specific Memory B Cells in Murine Hemophilia A.

The elimination of FVIII-specific memory B cells is an essential step in the design of new therapeutic strategies for the induction of immune tolerance in hemophilia A with FVIII inhibitors. Using a mouse model of hemophilia A we recently reported that low dose FVIII stimulates the differentiation of FVIII-specific memory B cells into antibody-secreting plasma cells whereas high dose FVIII inhibits this process. The inhibition of memory-B-cell re-stimulation is irreversible and seems to be due to an induction of apoptosis. Further understanding of the complex interactions that lead to either re-stimulation and differentiation of memory B cells or inhibition and eradication of these cells requires appropriate technologies for single-cell analysis and functional studies. We established a new technology for single-cell analysis and cell sorting of FVIII-specific murine memory B cells. A combination of magnetic bead separation and multi-color flow cytometry enabled us to analyze and purify FVIII-specific memory B cells obtained from hemophilic mice treated with FVIII. In a first step, we depleted undesirable cell populations (IgM+, IgD+, CD11c+, F4/80+, Gr1+ and CD49b+ cells) from total spleen cells by magnetic bead separation. In a second step, we used multicolor flow cytometry to exclude CD4+ T cells and analyze the FVIII-specific memory B cell compartment. This compartment was specified by staining the specific B-cell receptor with FVIII and anti-IgG antibodies. Frequencies of cells in this compartment ranged from 0.1–0.5% of total spleen cells in animals treated with 4 intravenous doses of FVIII, given at weekly intervals. We could not detect any FVIII-specific memory B cells in naïve mice. By means of single cell sorting we isolated FVIII-specific memory B cells for further functional studies. We were able to cultivate FVIII-specific memory B cells in microwell cultures in vitro and differentiate them into antibody-secreting plasma cells. The re-stimulation and differentiation of single-cell sorted memory B cells was strictly dependent on the presence of activated CD4+ T cells. CD4+ T cells obtained from naïve mice did not support the memory response. Furthermore, the re-stimulation and differentiation of memory B cells in the presence of activated CD4+ T cells did not require additional dendritic cells for antigen presentation. Obviously, memory B cells provide sufficient antigen presentation to CD4+ T cells to enable them to trigger the memory response. Our approach for single-cell analysis and purification of FVIII-specific memory B cells provides a new tool for tracking memory B cell populations in vivo and for directly analyzing the regulation of memory B cell function. It opens the field for future studies which should elucidate signals and molecules involved in activation or inhibition and eradication of FVIII-specific memory B cells. These activities will eventually lead to the identification of targets for the design of new treatment strategies for patients with FVIII inhibitors.

Genetically Attenuated Plasmodium berghei Liver Stages Persist and Elicit Sterile Protection Primarily via CD8 T Cells

Live-attenuated Plasmodium liver stages remain the only experimental model that confers complete sterile protection against malaria. Irradiation-attenuated Plasmodium parasites mediate protection primarily by CD8 T cells. In contrast, it is unknown how genetically attenuated liver stage parasites provide protection. Here, we show that immunization with uis3(-) sporozoites does not cause breakthrough infection in T and B-cell-deficient rag1(-/-) and IFN-gamma(-/-) mice. However, protection was abolished in these animals, suggesting a crucial role for adaptive immune responses and interferon-gamma. Although uis3(-) immunization induced Plasmodium-specific antibodies, B- cell-deficient mice immunized with uis3(-) sporozoites were completely protected against wild-type sporozoite challenge infection. T-cell depletion experiments before parasite challenge showed that protection is primarily mediated by CD8 T cells. In good agreement, adoptive transfer of total spleen cells and enriched CD8 T cells from immunized animals conferred sterile protection against malaria transmission to recipient mice, whereas adoptive transfer of CD4 T cells was less protective. Importantly, primaquine treatment completely abolished the uis3(-)-mediated protection, indicating that persistence of uis3(-)-attenuated liver stages is crucial for their protective action. These findings establish the basic immune mechanisms underlying protection induced by genetically attenuated Plasmodium parasites and substantiate their use as vaccines against malaria.

Immunisation with a major Trypanosoma cruzi antigen promotes pro-inflammatory cytokines, nitric oxide production and increases TLR2 expression

Innate and adaptive immunity collaborate in the protection of intracellular pathogens including Trypanosoma cruzi infection. However, the parasite molecules that regulate the host immune response have not been fully identified. We previously demonstrated that the immunisation of C57BL/6 mice with cruzipain, an immunogenic T. cruzi glycoprotein, induced a strong specific T-cell response. In this study, we demonstrated that active immunisation with cruzipain was able to stimulate nitric oxide (NO) production by splenocytes. Immune cells also showed increased inducible nitric oxide synthase protein and mRNA expression. Spleen adherent cells secreted high levels of IFN-γ and IL-12. Microbicidal activity in vitro was mainly mediated by reactive nitrogen intermediaries and IFN-γ, as demonstrated by the inhibitory effects of NO synthase inhibitor or by IFN-γ neutralisation. Specific T-cells were essential for NO, IFN-γ and TNF-α production. Furthermore, we reported that cruzipain enhanced CD80 and major histocompatibility complex-II molecule surface expression on F4/80+ spleen cells. Interestingly, we also showed that cruzipain up-regulated toll like receptor-2 expression, not only in F4/80+ but also in total spleen cells which may be involved in the effector immune response. Our findings suggest that a single parasite antigen such as cruzipain, through adaptive immune cells and cytokines, can modulate the macrophage response not only as antigen presenting cells, but also as effector cells displaying enhanced microbicidal activity with reactive nitrogen intermediary participation. This may represent a mechanism that contributes to the immunoregulatory process during Chagas disease.

The role of MHC-II in the maintenance of memory B cell function (B22)

Abstract By using conditional, B cell-restricted MHC-II-deficient mice (IA-B mice), we previously showed that antigen-specific memory B cells could be established but they then lost MHC-II expression due to ongoing cd19Cre-mediated deletion of the conditional iab allele, without significant loss in memory cell number. In this study, we examined whether or not MHC-II deficient memory B cells are functionally competent to differentiate into plasma cells. IA-B mice carrying a 4-hydroxy-3-nitro-phenyl-acetyl (NP) hapten-specific VH transgene (QM) were immunized with NP-coupled chicken gamma globulin plus alum. QM/IA-B mice generated NP+IgG+ memory B cells (~0.1% of total spleen cells), which subsequently lost MHC-II during maintenance. When cultured in the presence of 3T3 feeder cells with cytokines and various stimuli, both MHC-II(+) and MHC-II(−) NP+ memory B cells purified from QM/IA-B mice produced anti-NP IgG antibody upon LPS stimulation. However, anti-NP IgG production of MHC-II(−) NP+ memory B cells upon polyvalent B cell receptor stimulation with NP−Ficoll was significantly reduced compared to that of MHC-II(+) NP+ memory B cells. These results suggest that expression of MHC-II on memory B cells is required for maintenance of their capacity to differentiate into plasma cells in response to antigen stimulation. This work was supported by NIAMS AR052470 (M.S.) and NIAID AI47379 (P.A.K.).

Distinct Phenotype of Chronic Lymphocytic Leukaemia (B-CLL) Cells Engrafting in NOD/SCID Mice.

We have previously reported reliable engraftment of CD19/CD5/CD23/CD45 positive human B-CLL cells in the spleens of NOD/SCID mice (NSS-CLL cells) following transplantation of human peripheral blood-derived B-CLL (PB-CLL) cells. On histology, in the majority of the samples NSS-CLL cells formed focal aggregates which also contained various amounts (range:0–50%) of human CD45/CD3+ T cells (ASH 2005; #52). We now have further characterized these NSS-CLL cells. In our model 1x10^8 MNC are injected i.v. plus i.p. and engraftment in the spleen and other organs is analyzed after 4 (−8) weeks by flow cytometry and immunohistochemistry. In 22 CLL samples investigated in a total of 64 NOD/SCID mice 1.6±0.4x106 NSS-CLL cells representing 10.5±2.3% of total spleen cells were recovered with recovery highly reproducible on repetitive experiments (3.0 vs. 2.0; 1.6 vs. 1.5; 0.2 vs. 1.1; 0.0 vs. 0.0x106 NSS-CLL cells; n=4). In contrast to the low proliferative status reported for human PB-CLL, considerable proliferation was observed in NSS-CLL cells. Following the application of BrdU (1mg/6g d5 i.p., 1mg/ml added to drinking water d6–13; 20–27) BrdU positive NSS-CLL cells ranged from 5.3–25.0% (n=5). Immunohistological analysis showed positive staining for the proliferation marker Ki67 in 18.5±3.5% of NSS-CLL cells. In addition, markers related to proliferation/activation of B-CLL proliferation center cells such as survivin (mean MFI: 5.5±0.8 vs. 2.3±0.2; p=0.028; n=6) and CD100 (semaphorin 4d; mean MFI: 3.3±0.5 vs. 1.1±0.2; p=0.043; n=5) were significantly up-regulated in NSS-CLL vs. PB-CLL cells. When NSS-CLL cells were characterized utilizing additional adhesion/migration, differentiation and/or activation markers, only a subset of NSS-CLL cells (15.7±8.2%, n=6) expressed chemokine coreceptor (CCR) 7, while PB-CLL cells uniformly showed high CCR7 expression. Also CCR5, a migration marker in the context of non-Hodgkin lymphomas, consistently was demonstrated on a fraction of NSS-CLL cells (8.1±3.0%; n=6), whereas here no CCR5 expression was found on PB-CLL cells. No expression of human CD10, CD11c, CD127 or CD49d was detected in B-CLL cells derived from either PB- or NSS-CLL cells, while both sources, as expected, uniformly stained positive for CD40. In summary, NSS-CLL exibit a distinct phenotype as compared to PB-CLL cells and show considerable similarity to B-CLL cells in the proliferation centers of involved human tissues. For these cells not only proliferation but also increased expression of survivin and CD100 as well as down-regulation of CCR7 have been described. Therefore, we think that our model may represent a novel tool to further elucidate biological properties of human B-CLL and, in addition, may serve to devise and evaluate novel treatment strategies.

Immunomodulatory activity of polysaccharide isolated from Angelica sinensis

The immunomodulatory activities of an Angelica sinensis polysaccharide (AP), purified from the fresh root of A. sinensis Diels, were investigated in vitro in relation to the specificity to immune cells. AP consisted of rhamnose, arabinose, mannose, glucose, galactose with the molar ratio of 1.00:4.54:2.98:11.09:7.45. Cell proliferation results showed that proliferation of total spleen cells, macrophages and T cells were promoted by the action of AP. The treatment of AP increased the production of IL-2 and IFN-γ, while that of IL-4 was decreased. RT-PCR analysis displayed that the IL-2 and IFN-γ gene expression were enhanced but the IL-4 gene expression was decreased. Some differences in cytokines secretion pattern were also detected, the expression of IFN-γ was rapidly augmented while that of IL-2 responded later. The flow cytometry results showed that the percentage of CD4 +T cell in total spleen cells was remarkably increased by AP, while that of CD8 +T cell was slightly decreased. In conclusion, AP has immunomodulatory activity by regulating expression of Th1 and Th2 related cytokines. The time–effect relation of cytokines response also suggests that macrophages and natural killer cells involved in nonspecific immunity were primary activated, and helper T cell were secondarily affected by AP.

Natural killer T cells are required for the development of a superantigen‐driven T helper type 2 immune response in mice

We show, here, that one single injection or weekly injections of staphylococcal enterotoxin B (SEB), starting in 1-day-old newborn mice, induced a powerful immune response with a T helper type 2 (Th2) pattern, as judged by the isotype and cytokine profile, with the production of large amounts of SEB-specific immunoglobulin G1 (IgG1), detectable levels of SEB-specific IgE and increased production of interleukin-4 by spleen cells. These protocols also induced an increase in the levels of total IgE in the serum. Memory of SEB was transferred to secondary recipients by using total spleen cells from primed animals. The secondary humoral response in transferred mice was diminished if spleen cells from SEB-treated mice were previously depleted of CD3+ or Vbeta8+ T cells or NK1.1+ cells. In vivo depletion of NK1.1+ cells in adult mice resulted in a marked reduction in the SEB-specific antibody response in both the primary and secondary immune responses. Additionally, purified NK1.1+ T cells were able to perform SEB-specific helper B-cell actions in vitro and in vivo. These results suggest that NK1.1+ T cells are required for the full development of humoral immunological memory, whilst making neonatal tolerance to SEB unachievable.

Immune Regulatory Mechanisms Influence Early Pathology in Spinal Cord Injury and in Spontaneous Autoimmune Encephalomyelitis

Injuries to the central nervous system (CNS) trigger an inflammatory reaction with potentially devastating consequences. In this report we compared the characteristics of the inflammatory response on spinal cord injury (SCI) caused by a stab wound between the T7 and T9 vertebrae and spontaneous experimental autoimmune encephalomyelitis (EAE). SCI and EAE were compared in two types of myelin basic protein Ac1-11-specific T-cell receptor transgenic mice: T/R+ mice harbor regulatory T cells, and T/R- mice lack regulatory T cells. Our results show that 8 days after SCI, T/R- mice developed a strong T-cell infiltrate in the spinal cord, with remarkable down-modulation of CD4 expression that was accompanied by a local increase in Mac-3+ and F4/80+ reactivity and diffuse local and distal astrogliosis. In contrast, T/R+ mice exhibited a modest increase in CD4+ cells localized to the site of injury, without CD4 down-modulation; focal astrogliosis was restricted to the site of the lesion, although Mac-3+ and F4/80+ cells were also present. Similarly to T/R- mice that underwent SCI, T cells displaying down-modulated CD4 expression were found in the CNS of older T/R- mice afflicted by spontaneous EAE. Overall, our results suggest that common mechanisms regulate T-cell accumulation in CNS lesions of different causes, such as mechanic lesion or autoimmune-mediated damage.

The Mucosal Adjuvant Macrophage-Activating Lipopeptide-2 Directly Stimulates B Lymphocytes via the TLR2 without the Need of Accessory Cells

The macrophage-activating lipopeptide-2 (MALP-2) is an agonist of the TLR heterodimer 2/6, which exhibits potent activity as mucosal adjuvant, promoting strong humoral and cellular responses. Although B cells expressing TLR2/6 are potential targets, very little is known about the effect of MALP-2 on B cells. Studies were performed using total spleen cells or purified B cells from WT mice or animals deficient in TLR2, T cells, B cells, or specific subpopulations of B cells. They demonstrated that MALP-2 promotes a T cell-independent activation and maturation of B cells (mainly follicular but also B-1a and marginal zone B cells) via TLR2. MALP-2 also increased the frequency of IgM- and IgG-secreting cells, but bystander cells were required for IgA secretion. Activated B cells exhibited increased expression of activation markers and ligands that are critical for cross-talk with T cells (CD19, CD25, CD80, CD86, MHC I, MHC II, and CD40). Immunization of mice lacking T cells showed that MALP-2-mediated stimulation of TLR2/6 was unable to circumvent the need of T cell help for efficient Ag-specific B cell activation. Immunization of mice lacking B cells demonstrated that B cells are critical for MALP-2-dependent improvement of T cell responses. The knowledge emerging from this work suggests that MALP-2-mediated activation of B cells through TLR2/6 is critical for adjuvanticity. B cell stimulation by pattern recognition receptors seems to be a basic mechanism that can be exploited to improve the immunogenicity of vaccine formulations.

Oral exposure to atrazine modulates cell-mediated immune function and decreases host resistance to the B16F10 tumor model in female B6C3F1 mice

Atrazine (ATZ) is used throughout North America to control annual broadleaf weeds and grasses in various crops including; corn, sorghum, and sugar cane. Unfortunately, contamination of surface and ground water has occurred as a result of ATZ's chemical and physical properties, and its widespread use throughout the U.S. Midwest. A study of ATZ's immunomodulatory properties was conducted using female B6C3F1 mice and a panel of immune assays and host resistance models designed to evaluate cell-mediated and antibody-mediated immunity. Mice were administered ATZ by gavage (0, 24, 250, and 500 mg/kg/day) for 14 days then evaluated for immune responsiveness. ATZ treatment significantly increased the number of splenic CD8 + T cells, cytotoxic T cell and mixed leukocyte responses, and dose-dependently reduced host resistance to B16F10 melanoma. Thymus and spleen weights, total spleen cell numbers and fixed macrophage function was also reduced in mice that were exposed to ATZ. These results demonstrate that oral ATZ exposure is sufficient to alter cell-mediated immune function and disease resistance in female B6C3F1 mice.

Herpes simplex virus type-1 induces IFN-alpha production via Toll-like receptor 9-dependent and -independent pathways.

Type I IFN production in response to the DNA virus herpes simplex virus type-1 (HSV-1) is essential in controlling viral replication. We investigated whether plasmacytoid dendritic cells (pDC) were the major tissue source of IFN-alpha, and whether the production of IFN-alpha in response to HSV-1 depended on Toll-like receptor 9 (TLR9). Total spleen cells or bone marrow (BM) cells, or fractions thereof, including highly purified pDC, from WT, TLR9, and MyD88 knockout mice were stimulated with known ligands for TLR9 or active HSV-1. pDC freshly isolated from both spleen and BM were the major source of IFN-alpha in response to oligodeoxynucleotides containing CpG motifs, but in response to HSV-1 the majority of IFN-alpha was produced by other cell types. Moreover, IFN-alpha production by non-pDC was independent of TLR9. The tissue source determined whether pDC responded to HSV-1 in a strictly TLR9-dependent fashion. Freshly isolated BM pDC or pDC derived from culture of BM precursors with FMS-like tyrosine kinase-3 ligand, produced IFN-alpha in the absence of functional TLR9, whereas spleen pDC did not. Heat treatment of HSV-1 abolished maturation and IFN-alpha production from all TLR9-deficient DC but not WT DC. Thus pDC and non-pDC produce IFN-alpha in response to HSV-1 via both TLR9-independent and -dependent pathways.

Challenge of Trypanosoma cruzi chronically infected mice with trypomastigotes activates the immune system and reduces subpatent parasitemia levels.

Challenge of 1-yr Trypanosoma cruzi chronically infected mice with trypomastigotes results in a consistent reduction of parasite dissemination that correlates with spleen activation and increase in the anti-T. cruzi effector immune mechanisms. That is, parasite challenge results not only in elimination of the inoculum but also in a drastic decrease in basal subpatent parasitemia levels as revealed by transferring blood samples to immunosuppressed mice. Parasite elimination correlated with (1) a brief and intense burst in the ability of spleen cells to produce interferon-gamma, (2) an increase in total IgG2a-producing spleen cells, (3) higher parasite-specific IgG2a serum levels, and (4) an accumulation of non-B, non-T class II+ cells in the spleen. Furthermore, challenged, chronically infected mice had increased numbers of B, CD4+, and CD8+ large spleen cells. Besides reinforcing the activation of protective Th1 effector mechanisms, challenge with T. cruzi also induced Th2 effector molecules, such as interleukin (IL)-10 and IL-4, and IL-4-dependent IgG1. Our results are the first evidence that the immune system of T. cruzi chronically infected mice can be optimized in its ability to restrict parasite dissemination, opening the possibility that therapeutic vaccination could be used to reduce the parasite load and pathology of patients with chronic Chagas' disease.

Hematopoietic effect of ginsenoside Rg3 in ICR mouse primary cultures and its application to a biological response modifier

Ginsenoside Rg3, which is obtained as a by-product during the steaming of red ginseng, at 300 μg/ml enhanced the proliferation of the total spleen and bone marrow (BM) cells in both the cyclophosphamide (CYC)-treated and non-CYC-treated groups.

Phenotypic expression of pyruvate kinase deficiency and protection against malaria in a mouse model.

The recombinant congenic mouse strains AcB55 and AcB61 are extremely resistant to malaria (Plasmodium chabaudi AS) despite the presence of susceptibility alleles at the known Char1/Char2 resistance loci. Resistance in AcB55 and AcB61 is controlled by a locus on chromosome 3 (Char4) shown to be allelic with or tightly linked to a loss-of-function mutation in pyruvate kinase (Pklr). AcB55 and AcB61 show important splenomegaly prior to infection caused by the expansion of the red pulp, and display histological signs of extramedullary erythropoiesis in the liver. Examination of splenic cell populations by flow cytometry demonstrates elevated numbers of TER119-positive erythroid precursor cells (>30% of total spleen cells), while RNA expression studies show elevated expression of erythrocyte-specific transcripts such as globin, transferrin receptor, and Nramp2/Slc11a2 in the spleen of both strains. Hematological profiling in both strains is consistent with the presence of anemia as evidenced by low total erythrocyte counts, decreased hemoglobin, as well as abnormally high numbers of circulating reticulocytes (15-20%). These results strongly suggest that the mutant Pklr allele (Pklr(269A)) of AcB55/61 strains causes hemolytic anemia compensated by constitutive erythropoiesis, which in turn protects the mice against P. chabaudi infection. The possible molecular basis of the Pklr protective effect is discussed and is under current investigation in these two strains.

T lymphocyte dependence of the antibody response to 'T lymphocyte independent type 2' antigens.

With regard to their capacity for antibody induction, antigens can be classified as either T lymphocyte dependent (TD) or as T lymphocyte independent (TI).1 In the immune response to TD antigens, T lymphocyte help to B lymphocytes is essential for the regulation of B lymphocyte proliferation, production of immunoglobulins, immunoglobulin class switching, rescue of B lymphocytes from apoptotic death, germinal centre formation, and generation of B lymphocyte memory.2 In contrast to TD antigens, TI antigens induce antibody production without the help of T lymphocytes. TI antigens can be further divided into TI type 1 antigens (TI-1), which are polyclonal B lymphocyte activators (e.g. lipopolysaccharides), and TI type 2 (TI-2) antigens. TI-2 antigens are able to directly stimulate B lymphocytes. However, the antibody response to TI-2 antigens is somehow influenced by T lymphocytes.3 TI-2 antigens do not induce immunological memory and antibodies to TI-2 antigens in humans only develop after the age of 2 years.4,5 Generally, TI-2 antigens are antigens that consist of repetitive biochemical structures such as polymeric protein antigens, trinitrophenyl-ficoll (TNP-ficoll), and dinitrophenyl-ficoll (DNP-ficoll). A clinically important group among the TI-2 antigens are the bacterial capsular polysaccharides.6 Capsular polysaccharides of Streptococcus pneumoniae, Haemophilus influenzae and Neisseria meningitidis are responsible for the bacterial virulence and antibodies to capsular polysaccharides provide protection against invasive infections with these bacteria.7 The delay in antibody formation to encapsulated bacteria renders infants and young children highly susceptible to infections with encapsulated bacteria, especially from the ages of 4 to 6 months on, when the placentally derived maternal IgG is metabolized.5 Therefore, children younger than 2 years of age are more at risk for invasive infections caused by encapsulated micro-organisms.8 Children with a persisting defect in the production of antibodies specific for pneumococcal capsular antigens after this age have the so-called ‘specific antibody deficiency with normal immunoglobulins’ (SADNI). They suffer from recurrent pneumococcal infections, although their immunoglobulin and immunoglobulin subclass levels and responses to protein antigens are normal.9–12 It is estimated that 5–10% of the children referred for evaluation of recurrent infections have SADNI and it is therefore highly important to understand the immunological background of the antibody formation against TI-2 antigens.13 In this review we will summarize the current understanding of how T lymphocytes modulate the antibody response against TI-2 antigens.

Various cells of the immune system and intestine differ in their capacity to reduce hexavalent chromium

The cells of the immune system form a strong line of defence against foreign substances. The present study was undertaken to investigate the capacity of different cells of Wistar rats to reduce potentially carcinogenic hexavalent chromium (Cr-VI) into less toxic trivalent chromium in vitro. 5×10 6 cells were incubated with 10 or 25 μg ml −1 of Cr (VI) in the form of K 2Cr 2O 7 at 37°C in the presence of 5% CO 2 in air. At various time periods the remaining amount of Cr (VI) was measured and the percentage of Cr (VI) reduced was calculated. Among the single cell suspensions from the splenic cells a peak reduction of 55% was observed with the total spleen cells, 40% with the B-lymphocyte-enriched subpopulation, 10% with T-lymphocytes and 24% with the macrophages. The reduction by splenic and peritoneal macrophages was similar. Total thymocytes reduced 54% of the Cr (VI). Since the most common route of entry of chromium is through drinking water and food, intestinal cells were also investigated. Among the intestinal cells the maximum reduction of 100% (of 10 μg ml −1) was observed with the upper villus cells and 72% with the middle villus cells while reduction was the least (4%) with the crypt cells. The reduction in the intestinal loop in situ was 100%. The time taken by each cell type for the peak reduction to Cr (VI) was markedly different. The findings thus show that the capacity of different cells in the body differs vastly in their capacity and time taken to reduce hexavalent chromium. The most efficient handling of Cr (VI) by the intestine, due to the presence of a variety of cells and bacteria, protects the body from its adverse effects.

Respiratory exposure to diesel exhaust particles decreases the spleen IgM response to a T cell-dependent antigen in female B6C3F1 mice.

We investigated the systemic immunotoxic potential of respiratory exposure to diesel exhaust particles (DEP) in this study. Female B6C3F1 mice (approximately 8 weeks old) were exposed to increasing concentrations of DEP intratracheally, 3 times every two weeks, and sacrificed 2 or 4 weeks after the first exposure. The systemic toxicity and immune status in mice were evaluated. Mice exposed to DEP (1 to 15 mg/kg) showed no significant changes in body, spleen, or liver weights. Lung weights were increased in the mice exposed to 15 mg/kg DEP for 2 or 4 weeks. Except for a decreased platelet count, no significant alterations occurred in hematological parameters following DEP exposure. The number of splenic anti-sheep red blood cell (sRBC) IgM antibody-forming cells (AFC) decreased following DEP exposure for 2 weeks. This effect was less severe following 4 weeks of exposure and was only evident in the high dose group. Exposure to DEP also resulted in a significant decrease in the absolute numbers and the percentages of total spleen cells for total, CD4(+), and CD8(+) T cells, while the numbers of B cells and total nucleated cells in spleen were not significantly changed. The proliferative response of splenocytes to the T-cell mitogen, concanavalin A (ConA), as well as their production of IL-2 and IFN-gamma, was decreased dose-dependently following exposure of mice to DEP for 2 weeks, whereas proliferation was not changed in response to anti-CD3 monoclonal antibody. In summary, short-term respiratory exposure of mice to DEP resulted in systemic immunosuppression with evidence of T cell-mediated and possibly macrophage-mediated mechanisms.